Plastisols and propellants containing alkylene dihydrazines

ABSTRACT

5. In a solid rocket propellant grain comprising a fuel, oxidizer and binder the improvement which comprises a binder consisting essentially of a relatively non-volatile high nitrogen hydrazine substituted plasticizer material and a hydrophilic polymer, said plasticizer material being liquid at the temperature of formulating said composition and said hydrophilic polymer yielding an extensible, elastic material when blended with said plasticizer, the relative proportions of said plasticizer and said polymer ranging from about 15/1 to 1/3 on a weight basis, said binder being from about 10 to about 60 weight percent of the total propellant gain.

United States Patent Pannell [151 3,657,028 [451 Apr. 18,1972

[54] PLASTISOLS AND PROPELLANTS CONTAINING ALKYLENE DIHYDRAZINES [72] Inventor: Calvin E. Pannell, Lafayette, Calif.

[73] Assignee: The Dow Chemical Company, Midland,

Mich.

[22] Filed: Apr. 11, 1964 [21] Appl.No.: 367,606

[52] U.S.Cl ..'....149/19, 149/36, 149/109 UNITED STATES PATENTS 3,211,720 10/1965 Henbusch .,..149/36 X Primary Examiner-Benjamin R. Padgett Attorney-James B. Vander Kelen and C. Kenneth Bjork EXEMPLARY CLAIM 5. In a solid rocket propellant grain comprising a fuel, oxidizer and binder the improvement which comprises a binder consisting essentially of a relatively non-volatile high nitrogen hydrazine substituted plasticizer material and a hydrophilic polymer, said plasticizer material being liquid at the temperature of formulating said composition and said hydrophilic polymer yielding an extensible, elastic material when blended with said plasticizer, the relative proportions of said plasticizer and said polymer ranging from about 15/1 to H3 on a weight basis, said binder being from about 10 to about 60 weight percent of the total propellant gain.

6 Claims, No Drawings PLASTISOLS AND PROPELLANTS CONTAINING ALKYLENE DHIYDRAZHYEQ The invention herein described was made in the course of or under a contract or subcontract thereunder with the Department of the Air Force.

This invention relates to plastisol compositions and more particularly is concerned with a novel plastisol having a reducing character which is particularly suitable for use as a binder for solid propellants.

In the rocket and missile art, an ideal solid propellant composition is considered to be a fuel-oxidant mixture which not only is able to meet the diverse requirements of formulation and fabrication but also possesses the requisite strength to retain a predetermined configuration under flight and combustion conditions. Fuels and oxidizers alone cannot on a practical basis be fabricated into a propellant grain having good strength and structural characteristics. To fabricate solid propellants which meet the requirements for strength and configuration stability, binder materials must be employed. Conventionally, plastisol binders such as solid polymeric nitrocellulose or polyvinyl chloride plasticized with relatively nonvolatile liquid oxidants such as nitroglycerine, triethylene glycol dinitrate or trimethylolethane trinitrate are employed. Although the resultant propellant compositions possess good strength and structural characteristics, the use of these conventional binders lowers the impulse over that which would be achieved by use of the fuel-oxidizer alone.

Now, unexpectedly a novel binder composition for solid propellants has been found which possesses a higher energy than the conventionally employed binders as well as serves to provide excellent strength and structural characteristics in the fabricated propellant grain.

It is a principal object of the present invention to provide a novel plastisol binder for propellants employing non-oxidizing plasticizers.

It is another object of the present invention to provide a high energy binder for solid propellants which has desirable high nitrogen to carbon and hydrogen to carbon ratios resulting in lower molecular weight exhaust gases and hence a higher I,,,.

It is a further object of the present invention to provide a plastisol binder which imparts good tensile strengths to cured compositions of fuel, oxidizer and binder as well as gives uncured compositions having viscosities which permit the necessary operations of mixing and casting during propellant grain fabrication.

It is another object of the present invention to provide a novel binder composition which exhibits a high elongation thus providing a flexibility which leads to good characteristics during thermal cycling and resistance to cracks on ignition.

It is also an object of the present invention to provide a novel plastisol binder composition the physical properties and energy contents of which are such that a minimal decrease in thrust results when the binder is incorporated into a propellant composition.

These and other objects and advantages readily will become apparent from the detailed description presented hereinafter.

The present novel plastisol composition in general comprises a relatively non-volatile high-nitrogen hydrazine substituted plasticizer material which is liquid at the formulating temperature and a hydrophilic polymer which dissolves in, is swelled by or reacts with the high-nitrogen hydrazine material to yield extensible, elastic or rubbery materials.

More particularly the present novel compositions employ as plasticizer a relatively non-volatile hydrazine material such as alkylene hydrazines corresponding to the general formula where n is an integer from 1 to 6 and having at least one hydrazine group f or each carbon atom in the carbon chain. (Ethylene dihydrazine,

10 are representative species of such alkylene hydrazines.) Glycerol d1- pentaerythritol tetrahydrazine [C(CHs-NHNHDJ, dihydrazino noetone hydrazone IIIHNH; bl] HNH, (H2 C C- C Hz l NNH:

3-hydrazin0-2-hydroxy-proploneldehyde hydrazono ITIHNH, I1 NNH IC CCH and hydrazinoacetaldehyde hydrazone NNH,

are suitable hydrazine materials for use as the plasticizer in the present composition. Ethylene dihydrazine is a preferred plasticizer.

Hydrophilic polymers to be used in the present novel composition are those materials that are soluble in water, lower aliphatic alcohols containing up to about three carbon atoms, amines and hydrazine-substituted materials. Additionally polymers which will react with the hydrazine plasticizers to form swellable or soluble products also can be used. Illustrative examples of suitable polymers which are soluble or swell directly in the hydrazine plasticizer are polyacrylamides, polyvinyl alcohol, cellulose acetate, cellulose acetate-butyrate, polyvinylforrnal, polyethyleneirnine, polyethylene hydrazine, ethylene polyamine, methyl cellulose, hydroxyethyl cellulose, oxidized cellulose, polyethylene oxide, polypropylene oxide and the like. Copolymers such as polyvinyl alcohol with polyvinyl acetate also can be used. 50 Other polymers which do not swell or dissolve directly when mixed with the plasticizer but which can be modified so as to be made plasticizable by the hydrazine material can also be used. For example, the surface of polyacrylic acid reacts with ethylene dihydrazine and crosslinks to such an extent that any appreciable dissolution or swelling of the polymer in this plasticizer is prevented. However, when this polymer is modified by neutralization with hydrazine, the resulting salt gives a suitable plastisol with ethylene dihydrazine.

Other modifiable polymers which can be employed are those containing groups reactive to Nl-l--bonds. Examples are aldehyde polymers from acrolein, dialdehyde starch, acidic high nitrogen polymers such as polyvinyl tetrazole, nitrile containing polymers such as polyacrylonitrile, modified polyurethanes soluble starches and cellulose and the like.

Polyacrylamides are preferred forms of polymers to use in the present composition.

The plasticizer to polymer proportions used in the novel plastisol composition depend on the desired properties in the resultant product. In general for a given polymer with a lower energy content than the plasticizer, the higher the proportion of plasticizer to polymer the weaker in structural strength will be the final plastisol. At the same time, however, as the ratio of plasticizer to polymer increases the energy content of the plastisol also increases. From the practical standpoint, the end use requirements of the propellant grain will to a large degree also define the required physical strength in a cured grain. A principal advantage of the present composition is that it provides a binder having a high elongation and flexibility. This binder therefore gives good characteristics during thermal cycling and resistance to cracks on ignition. Additionally, the initial high elongation provides more latitude for cross-linking.

In practice the proportions of plasticizer to polymer ordinarily range from about 15/1 to US on a weight basis. Preferably, the plasticizer/polymer ratio ranges from 3 to 12 on a weight basis.

In use of the resulting plastisol as a binder for a solid rocket propellant system the binder is mixed with the fuel, oxidizer and other additives that may be employed. These are blended, poured, and cast, pressed, or extruded into a predetermined propellant grain configuration. The grain is cured and subsequently treated in a conventional manner. The binder will be used in an amount of from about to about 60 weight percent of the total propellant grain, depending upon energy and strength requirements of the grain as discussed hereinbefore.

The present novel binder composition can be used in fabricating propellant grains having oxidizers and fuels selected from a wide variety of materials employed in such compositions.

For example oxidizers such as ammonium perchlorate, coated nitronium perchlorate, ammonium nitrate, coated hydrazine nitroforrnate, hydrazine perchlorate, lithium perchlorate and the like all can be blended with the present novel binder. Similarly particulate metal fuels such as aluminum and lithium, light metal hydrides such as lithium hydride, aluminum hydride, beryllium hydride, lithium aluminum hydride, organic nitrogen-hydrogen fuels having high N/C ratios such as triaminoguanidinium azide, 5- aminotetrazole, amino diaminotetrazene, triaminoguanidinium azide, hydrazine azide double salt, lower guanidine azide salts such as diarninoand monoaminoguanidinium azide and the like.

The following Examples will serve to further illustrate the present invention but are not meant to limit it thereto.

Example 1 A number of tests were carried out to evaluate the effectiveness of ethylene dihydrazine as a plasticizer for high molecular weight hydrophilic polymers.

in these studies, about 5 percent by weight of a polymeric material was introduced into ethylene dihydrazine and its dissolution characteristics noted. Table l, which follows, presents the results of these studies.

TABLE 1 Run Number Polymer Remarks 1 Polyacrylamide (about Polymer swelled to occupy 1,000,000 molecular volume of test vessel. Resultweight). ing product was strong after curing. 2 Polyvinyl alcohol Very soluble: higher solids content needed for high strength in cured product. 3 Methylcellulose (-1,500 Do. centipoise viscosity).

4 Polyethylenimine Polymer soluble; terms viscous (-30,000-40,000 molecsolution. ular weight).

6 Polyethylene hydrazlne. Do.

6. Polyammonium acrylate Polymer soluble.

7 Hydroxyethylcellulose. Polymer soluble; higher solids required to yield strong specimen.

Example 2 A number of binders of the present invention were prepared. The resulting compositions were cast in a dumbbell shaped mold and cured at a predetermined temperature. Tensile tests were run on the cast samples using an Instron Tensile Tester at 2 inches per minute cross-head speed strain rate.

Sample compositions, cure times and temperatures and tests results are presented in Table 11.

TABLE II Physical properties of etthiylgnedlhydrazine-polyacrylamlde n or Elongation Plasticizer/ Temp., Maximum at maximum polymer 16 hr. tensile tensile Maximum (proporcure, C. strength, strength, elongation, Run Number Type of polyacrylamide tions) p.s.i. percent percent 1 Commercial form 1/1 72 28. 9 264. 8 280. 8 Highly crossllnked 1/1 72 616. 0 233. 8 235. 0 Crosslinked 3 1/1 72 289. 5 183. 0 184. 0 4 Highly crossllnked 2/1 72 26. 3 335. 0 339.5

1 Commercial polyacrylamide heated for 3 hours at 150 C.

Triaminoguanidinium azide has been found to be particularly useful in that this material is soluble in ethylene dihydrazine. Additionally, it is able in the case polyacrylamides to effect cross-linking upon curing thereby to provide a high tensile strength in the cured grain without interfering with the necessary uptake of ethylene dihydrazine.

The reducing fuel type binders of the present invention are uniquely adapted for use in the solid fuel section of hybrid type rockets where the oxidizer is stored separately from the fuel and controllably fed onto the combustion surface of the fuel. The highly desirable start-stop feature of this type of rocket requires the omission of oxidizers from the solid fuel composition as well as a hypergolic reaction between oxidizer and fuel material. In conventional practice, fuel-rich propellant grains are used in such hybrides to avoid ignition problems in on-off operation because conventional hybrid binders are not hypergolic with oxidizers. Ethylene dihydrazine is hypergolic with N 0 ClF and the like oxidizers thereby providing the additional advantage that the present binder system can be used satisfactorily in on-off solid propellant systems.

Example 3 a. About 8 parts by weight ethylenedihydrazine, about 1 part by weight commercial slightly hydrolyzed high molecular weight polyacrylamide and about 18 parts by weight potassium chloride, as an inert filler to simulate an inorganic oxidizer, were thoroughly mixed and the resulting fluid slurry poured into a dumbbell mold. The casting was heat cured at about 72 C. for about 72 hours. The specimen was tested using the lnstron tester at the 2 inches per minute strain rate. This cured propellant grain" had a maximum tensile strength to yield of 9.35 pounds per square inch. The elongation at this point was 24.6 percent.

b. Another composition consisting on a weight basis of 1 part of this same type polyacrylamide, 8 parts ethylene dihydrazine, 1 part triaminoguanidinium azide and 18 parts inert potassium chloride as simulated oxidizer was similarly blended, cast and cured. The resulting cured specimen when tested on the lnstron tester at 2 inches per minute cross-head speed showed a tensile strength of 21.2 pounds per square inch and an elongation of 38.4 percent at the yield point.

e. Cured east grains were prepared using the same formulation described directly for the preceding test except that the triaminoguanidinium azide content was increased to 2 parts by weight. Testing of this sample'in the lnstrom at the same crosshead speed indicated a tensile strength of 50 pounds per square inch and an elongation of 27.6 percent at the yield point.

d. About parts by weight ethylene dihydrazine, 1 part by weight of the polyacrylamide, 2 parts by weight triaminoguanidinium azide and 22 parts by weight of the potassium chloride dummy oxidizer were blended, cast and cured for 1 12 hours at 72 C. lnstron testing as before showed a tensile strength of pounds per square inch and an elongation of 21 percent at the yield point.

e. About 13 parts triaminoguanidinium azide, 8 parts ethylenedihydrazine, 1 part polyacrylamide and 18 parts potassium chloride filler (all on a weight basis) were blended, cast and cured for 18 hours at 72 C. This large amount of the triaminoguanidinium azide in the composition aided to promote curing and also provide large amounts of hydrogen and nitrogen in the binder which give a more energetic system. (The N/C ratio of the binder for this composition is 3.8.) The lnstron test at 2 inches per minute strain showed the cured product had a tensile strength of 10 pounds per square inch and an elongation of 63 percent at the yield point.

f. Methylcellulose (1 part by weight), ethylene dihydrazine (5 parts by weight) and potassium chloride tiller (8 parts by weight) were mixed, cast and cured as a dumbbell specimen. The curing cycle was 72 hours at 52 C. followed by 48 hours at 72 C. The cured product was tested on the lnstron tester at a cross-head speed of 2 inches per minute. The tensile strength of the product was 14.5 pounds per square inch and the elongation was 20 percent at yield.

g. Poly(vinyl alcohol) about 1 part by weight, ethylene dihydrazine about 4 parts by weight and potassium chloride oxidizer simulant," about 9 parts by weight were mixed, cast and cured in the same manner as described for the run 4(f). The resulting rigid product was found to resist bending and stretching when tested by hand to an extent comparable to the product produced in run 4(f).

Potassium chloride was used to simulate the oxidizer in the preparation of these compositions since this material has characteristics and physical form similar to the commonly used metal perchlorate and ammonium perchlorate oxidizers. The resulting products contained a realistic binder content as is found in actual propellant grains.

Example 4 A number of fuel-binder compositions were prepared by blending aluminum hydride, ethylene dihydrazine and a highly cross-linked polyacrylamide. Additionally, in certain of the formulations, a portion of the ethylene dihydrazine was replaced with a polymeric pyrolysis product produced by heating together malononitrile and triaminoguanidinium azide, hereinafter for purposes of ready identification referred to as Malonitaz. The resulting fluid blends were cast in the dumbbell mold, cured for 16 hours at a predetermined temperature. The rubbery appearing cured products were tested on the lnstron tester at cross-head strain rate speeds of 2 inches per minute and 20 inches per minute. Formulation data and the tensile properties and elongations for these products are presented in Tables III a and ill b.

TABLE IIIa Ethylene dihydrazine-polyacryIamide-AIH: formulations Composition Ethylene Weight percent dihydrazine/ Ethylene Poly- Alupolyacryl- Cure Run dihyacrylninum Maloamide temp. Number drazine amide hydride nitaz (ratio) C.

TABLE IIIb Properties of cured product Elongation at Maximum tensile maximum tensile Maximum elongastrength, p.s.i. strength, percent tion. percent Run 2 in./ 20 in./ 2 in./ 20 in./ 2 in./ 20 in./ min. min. min. min. min. min.

All values for tensile strength were calculated using the original cross-sectional area of the sample. During the test, this area does not remain constant; in fact it becomes quite small at the high elongations. Therefore, if the stress were cal culated for the actual cross-sectional area of the sample at the point of maximum tensile strength, these values would be considerably higher than shown in Table 111.

Example 5 A propellant composition consisting on a weight basis 27 percent ethylene dihydrazine, 2.7 percent polyacrylamide, 21.9 percent aluminum hydride and 48.4 percent ammonium perchlorate was used in end burning uncured motors. About 30 gram charges were burned. in duplicate runs, this composition gave measured impulses (lbf. sec./lbm.) of 179.7 and 206.4. The respective efficiencies were 69.2 and 76.1 percent.

As a control a commercial end-burning engine having a propellant consisting on a weight base of 37.3 percent triethylene glycol dinitrate, 16.7 percent ball powder, 15 percent ammonium perchlorate, 30'percent aluminum and l percent resorcinol was found to have an impulse of 167.9 and an efficiency of 66.4 percent.

Example 6 A number of propellants were fabricated using the present novel binder and various fuels and oxidizers. The composition data and calculated burning temperatures and specific impulses for a number of these propellants are presented in Table IV.

TABLE IV Propellant formulations and combustion characteristics of these components Weight, percent Combustion Ethylene characteristics dihy- 'Iridrazin amino- Ammo- Hydra- Compoly Ethyl- Polygueni- Alumi- Berylnium Nitron- Hexazinium bustion acrylene dihyacryldinium Alumiuum Beryllium perium pernitro' nitrotemp., Impulse, amide Run No. drazine amide azide num hydride lium hydride chlorate chlorate ethane iormate K. sec. (ratio) 27. 3 2. 7 3, 579 302. 1 10 11. 5 1. 3, 660 303. 2 9. 6 11. 5 1. 3,051 287. 1 9. 6 16. 7 3. 3, 113 288. 1 5 l0. 0 5. 3, 627 299. 3 2 15.0 7. 3, 676 296. 9 2 27. 3 2. 2, 682 282. 3 10 11. 6 1. 2, 956 290. 0 9. 6 18. 2 1. 3, 674 303. 1 10 13. 3 6. 3, 698 297. 0 2 22. 7 2. 3, 351 273. 7 10 26.0 5. 3,104 290. 0 5 15. 4 V 1. a 291 .1 10

Weight, percent Combustion Ethylene characteristics dihyamlno- Ammo- Hydra- Compoly- Ethyl- Polyguani- I Alumi- Berylnium Nltron- Hexazinium bustlon acrylene dihyacryldinlum Alurmnum Beryllium perium pernitronitrotemp., Impulse, amide Run No. drazme amide azide num hydride lium hynride chlorate chlorate ethane fomiate K. sec. (ratio) 36. 4 3. 6 12 3, 453 303. 9 10 In a manner similar to that described for the foregoing Examples, the other hydrazine containing plasticizers disclosed herein can be used with the disclosed polymers to provide reducing binders for use in propellants.

Various modifications can be made in the present invention without departing from the spirit or scope thereof for it is understood that I limit myself only as defined in the appended claims.

lclaim:

l. A plastisol composition which comprises a relatively nonvolatile high-nitrogen, hydrazine-substituted plasticizer material and a hydrophilic polymer, said plasticizer material being liquid at the temperature of formulating said composition and said hydrophilic polymer yielding an extensible material when blended with said plasticizer, the relative proportions of said plasticizer and said polymer ranging from about l to H3 on a weight basis.

2. A curable plastisol composition suitable for use as a binder for a rocket propellant which comprises a plasticizer selected from the group consisting essentially of a. an alkylene hydrazine having a carbon chain length of from one to six, and having at least one hydrazine group for each carbon atom in the carbon chain,

b. glycerol dihydrazine,

c. pentaerythritol tetrahydrazine,

d. dihydrazino acetone hydrazone,

e. 3 hydrazino-2-hydroxypropionaldehyde hydrazone, and

f. hydrazinoacetaldehyde hydrazone and a hydrophilic polymer selected from the group consisting essentially of 21,. polyacrylamide,

b polyvinyl alcohol,

c cellulose acetate,

d cellulose acetate-butyrate,

e polyvinyl formal,

f polyethyleneimine g. polyethylenehydrazine,

h. ethylene polyarnine,

i. methyl cellulose,

j. hydroxyethyl cellulose,

k. oxidized cellulose,

l. polyethylene oxide,

m. polypropylene oxide,

n. aldehyde polymers from acrolein o. dialdehyde starch,

p. polyvinyl tetrazole,

q. polyacrylonitrile, and

r. modified polyurethane,

s. soluble starches and cellulose the weight proportions of said plasticizer/polymer ranging from about l5/l to H3.

3. A curable plastisol composition which comprises ethylene dihydrazine plasticizer and polyacrylamide polymer in weight proportions of said plasticizer/polymer from about 15/ l to H3.

4. The composition as defined in claim 3 wherein the plasticizer/polymer ratio ranges from about 3 to 12.

5. In a solid rocket propellant grain comprising a fuel, oxidizer and binder the improvement which comprises a binder consisting essentially of a relatively non-volatile high nitrogen hydrazine substituted plasticizer material and a hydrophilic polymer, said plasticizer material being liquid at the temperature of formulating said composition and said hydrophilic polymer yielding an extensible, elastic material when blended with said plasticizer, the relative proportions of said plasticizer and said polymer ranging from about 15/1 to H3 on a weight basis, said binder being from about 10 to about 60 weight percent of the total propellant grain.

6. The solid rocket propellant grain as defined in claim 5 wherein the binder consists essentially of ethylene dihydrazine plasticizer and polyacrylamid polymer in weight proportions of said plasticizer/polymer from about l5/ 1 to l /3. 

1. A plastisol composition which comprises a relatively non-volatile high-nitrogen, hydrazine-substituted plasticizer material and a hydrophilic polymer, said plasticizer material being liquid at the temperature of formulating said composition and said hydrophilic polymer yielding an extensible material when blended with said plasticizer, the relative proportions of said plasticizer and said polymer ranging from about 15/1 to 1/3 on a weight basis.
 2. A curable plastisol composition suitable for use as a binder for a rocket propellant which comprises a plasticizer selected from the group consisting essentially of a. an alkylene hydrazine having a carbon chain length of from one to six, and having at least one hydrazine group for each carbon atom in the carbon chain, b. glycerol dihydrazine, c. pentaerythritol tetrahydrazine, d. dihydrazino acetone hydrazone, e. 3 hydrazino-2-hydroxypropionaldehyde hydrazone, and f. hydrazinoacetaldehyde hydrazone and a hydrophilic polymer selected from the group consisting essentially of a1. polyacrylamide, b1. polyvinyl alcohol, c1. cellulose acetate, d1. cellulose acetate-butyrate, e1. polyvinyl formal, f1. polyethyleneimine g. polyethylenehydrazine, h. ethylene polyamine, i. methyl cellulose, j. hydroxyethyl cellulose, K. oxidized cellulose, l. polyethylene oxide, m. polypropylene oxide, n. aldehyde polymers from acrolein o. dialdehyde starch, p. polyvinyl tetrazole, q. polyacrylonitrile, and r. modified polyurethane, s. soluble starches and cellulose the weight proportions of said plasticizer/polymer ranging from about 15/1 to 1/3.
 3. A curable plastisol composition which comprises ethylene dihydrazine plasticizer and polyacrylamide polymer in weight proportions of said plasticizer/polymer from about 15/1 to 1/3.
 4. The composition as defined in claim 3 wherein the plasticizer/polymer ratio ranges from about 3 to
 12. 5. IN A SOLID ROCKET PROPELLANT GRAIN COMPRISING A FUEL, OXIDIZER AND BINDER THE IMPROVEMENT WHICH COMPRISES A BINDER CONSISTING ESSENTAILLY OF A RELATIVELY NON-VOLATILE HIGH NITROGEN HYDRAZINE SUBSTITUTED PLASTICIZER MATERIAL AND A HYDROPHILIC POLYMER, SAID PLASTICIZER MATERIAL BEING LIQUID AT THE TEMPERATURE OF FORMULATING SAID COMPOSITION AND SAID HYDROPHILIC POLYMER YIELDING AN EXTENSIBLE, ELASTIC MATERIAL WHEN BLENDED WITH SAID PLASTICIZER, THE RELATIVE PROPORTIONS OF SAID PLASTICIZER AND SAID POLYMER RANGING FROM ABOUT 15/1 TO 1/3 ON A WEIGHT BASIS, SAID BINDER BEING FROM ABOUT 10 TO ABOUT 60 WEIGHT PERCENT OF THE TOTAL PROPELLANT GAIN.
 6. The solid rocket propellant grain as defined in claim 5 wherein the binder consists essentially of ethylene dihydrazine plasticizer and polyacrylamid polymer in weight proportions of said plasticizer/polymer from about 15/1 to 1/3. 